Composite pistons



p 9, 1969 F. c. TROMEL 3,465,651

COMPOSITE PI STONS Filed Feb. 15, 1968 3 Sheets-Sheet 1 FIGI.

FIG.2.

INVENTOR.

FREDERIC C. TROMEL ATTORNEY BY 3W.

Sept. 9, 1969 F. c. TROMEL I 3. 65

COMPOSITE PISTONS I Filed Feb. 13', 1968 3 Sheets-Sheet 2 1 f" us so 28 3| 29 26 1:

F IG. 5.

. INVENTOR.

19 FREDERlC c.1aous1.

BY BMH- ATTORNEY Sept- 9, 1969 F. c. TROMEL 3,465,651

COMPOSITE PISTONS Filed Feb. 13. 1968 3 Sheets-Sheet 3 3 l\b l|b 3 29b 26b F I G. 7.

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INVENTOR. FREDERIC c. TRO MEL ATTORNEY United States Patent OT" 3,465,651 COMPOSITE PISTONS Frederic C. Tromel, Schenectady, N.Y., assignor to Alco Products, Inc., New York, N.Y., a corporation of Delaware Filed Feb. 13, 1968, Ser. No. 705,150 Int. Cl. F01b 31/08; F02f 3/22; F04b 39/06 US. Cl. 92-186 Claims ABSTRACT OF THE DISCLOSURE Composite oil cooled piston to be subjected to high temperature in reciprocating devices wherein the piston has a body portion made of aluminum alloy and the like materials and a cap portion of ferrous alloy having a relatively thin crown, the body and cap being provided with connecting means and seating means therebetween so that in assembled position the cap will be stressed and the body portion and cap portion of the piston provided with passages and spaces to efficiently cool the crown of the cap during operation and to facilitate removal of the cap portion from the body portion of the piston.

The principle of using composite or multi-part pistons in which each of the respective parts are of different materials is well known. The materials selected for use in such pistons are chosen on the basis of their mechanical and physical properties to best meet the operating requirements of compressors, engines or other devices in which they are used. For example, an aluminum alloy piston body and a ferrous alloy cap is one known combination of different material which has been found to work very well.

Aluminum was frequently selected for use in pistons because it is light in weight and has excellent bearing properties. This permits the skirt of the piston body to slide easily in the cylinder liner and facilitates the oscillating action of the wrist pin in the piston body. However, aluminum has a relatively high coefficient of expansion and low strength at high temperatures and accordingly presents problems when all aluminum alloy pistons are used in direct contact with the high temperatures that prevail in the cylinders of internal combustion engines.

In order to meet this problem, prior art devices first utilized coo ing techniques such as introducing oil into the piston or oil spray in the piston crown on the side remote from the high temperatures that the piston encounters during operation. These oil cooled pistons were further improved by making them in composite form that is using an aluminum alloy piston body and a ferrous alloy cap at the end of the piston which would be in contact with the high temperatures developed in the coacting chamber. Oil cooled composite pistons are illustrated in US. Patents 3,323,503, 3,029,112, 2,759,461, 2,429,956 and 2,194,097.

Ferrous alloy caps are generally made of steel or cast iron and serve to protect the aluminum bodies from the adverse effect of the excessive heat encountered in such cylinders during operation. They adapt well for this function because they retain high strength at the operating temperatures and further can be designed to receive piston rings because the piston ring grooves cut into the steel or cast iron resist pounding out and wear.

However, caps of ferrous alloy as used in the prior art devices have many disadvantages. Such caps have high specific weight and low thermal conductivity and these characteristics lead to excess thermal stresses particularly where the parts are irregularly shaped and where the wall thickness is relatively heavy namely, that thickness of the crown portion of the cap between the outer surface there- 3,465,651 Patented Sept. 9, 1969 of exposed to the extremes in temperatures from the combustion gases, and the inner surface in contact with oil or crank case gases.

Thermal stresses produce piston part failure and other adverse conditions as a result thereof.

The present invention concerns itself with compensating for these disadvantages of the ferrous alloy cap used in the prior art devices but seeks to retain the desirable qualities and advantages of such caps when used in composite pistons.

This is accomplished by introducing opposing forces or stresses between the main body and the cap member of an oil cooled composite piston on the side remote from the working forces acting on the piston.

Summary of the invention Thus, the present invention covers an improved oil cooled composite piston including a light weight main body, a cap member mounted in operative relation to said main body and having a crown and a skirt; spaced seating means disposed between said body and said crown and connecting means for connecting the cap member to the main body whereby the connecting means will force said seating means into engagement and thereby stress the crown in assembled position to increase its load carrying capacity.

Additionally, the present invention contemplates a piston in which the cap member is dimensioned and coacts with a seating means in the piston whereby on proper tensioning of a central stud integral with the cap member the crown of the cap member will be placed in a prestressed condition prior to placing the piston into normal use or operation and the forces acting on the crown will be transmitted through the annular faying surfaces forming said seating means.

Additionally, the present invention provides in assembled position an interference fit between the skirt of the cap member and the main body and passage means or spaces between the cap member and the body and in the body so that cooling fluid can be readily introduced between the cap and the body portion to more efficiently cool the cap and the body during operation.

Certain passages for hydraulic fluid in the main body are also designed to facilitate easy disassembly of the cap member and main body of the piston.

Objects and advantages Accordingly, it is an object of the present invention to provide an oil cooled composite piston including a light weight main body portion and a relatively thin walled cap dimensioned and arranged to provide a piston relatively lower in weight, more efliciently cooled and adapted to avoid structural failure when subjected to high operating temperatures.

It is another object of the present invention to provide an oil cooled composite piston in which the piston body and cap member thereof are constructed and associated with means to increase the stresses between these elements so as to increase the load carrying capacity of the crown portion of the cap and to reduce excess thermal stresses between the parts of the piston.

It is another object of the present invention to provide a cap for a composite piston in which the crown portion of the cap is integral and not subjected to dangerous leakageof combustion gas into the crank case of the engine in which the piston is operated.

It is another object of the present invention to provide an oil cooled composite piston in which the body portion and the cap portion of the piston are so constructed that in assembled position the cooling chambers which receive cooling fluid therein are in close propinquity to the side 3 of the crown remote from the side in contact with high temperatures when the piston is in use.

These and other objects and advantages of the invention will become evident from the following description with reference to the accompanying drawings in which:

FIGURE 1 is a vertical section of a piston incorporating the present invention;

FIGURE 2 is an exploded view in cross section showing the components before assembly;

FIGURES 3, 4, and 5 are cross sectional views of a portion of a piston on an enlarged scale illustrating the sequence of seating the crown on the piston body during assembly, the clearances being greatly exaggerated; and,

FIGURES 6, 7, 8, and 9 are diagrammatic views illustrating different ways of providing the necessary clearances to produce a piston in accordance with this invention.

Referring to the drawings FIGURES 1 and 2 show a main body 10 and a cap member 11 of the composite piston forming the subject matter of the present invention.

The main body 10 is composed generally of light weight material such as aluminum or aluminum alloy. It is reduced in diameter for a spaced distance along the portion of the main body in assembled position adjacent the cap member to form a shoulder 12 and cut or grooved as at 13 about the periphery of the cap end. The axially extending surface 14 on the main body substantially adjacent the shoulder 12 is tapered or formed in cross section as a section of a cone. The purpose for tapering the axially extending surface 14 will appear clear from the description which follows and the function of the groove 17 will be made clear hereinafter.

The cap is preferably made by machining a forging of heat treated high strength steel in a solid of revolution to form a relatively thin crown 15 and an annular skirt or ring carrying portion 16.

A plurality of ring grooves 17 are provided in the outer annulus of the skirt 16 and the inner annulus 18 of the skirt will be tapered or formed in cross section as a section of a cone such that in assembled position the end of the skirt 19 will engage the shoulder 12 and the inner annulus 18 thereof will form an interference fit with the tapered axially extending wall 14 at the cap end of the main body of the piston.

Forming the cap member in a solid of revolution is preferred as this permits an analysis of the distribution of the all stresses on the cap during operation and suitable compensation therefor in the construction of the cap to minimize these stresses.

In the present invention such analysis and compensation allows for the formation of a relatively thin crown which reduces the weight of the piston and also permits more effective and efficient cooling thereof during operation.

The cap member 11 is provided or formed with a stud or connecting member 20 extending from the inner wall I of the crown portion 15 in the central axis of the piston. The stud is shown as integral with the crown to maintain the integrity and the strength of the crown portion 15.

The stud or connecting member 20 is threaded as at 21 and is adapted in assembled position to fit and extend through an oversized bore 22 in the main body 10.

As shown in FIGURES 1 and 2 when in assembled position, the stud or connecting member 20 receives about the threaded end a spacer 23, a plurality of resilient type washers 24 and a nut means 25 that can be tightened onto the threaded portion 21 so as to move the cap member and hold the same in tight engagement with the main body 10 of the piston.

The load carrying capacity of the cap member 11 and the piston are greatly increased by introducing prestresses in the crown 15 of a magnitude comparable to the stresses the crown and piston will meet in operation.

Accordingly, an essential feature of the present invention is to accurately provide controlled contacting seating surfaces between the main body 10 and the cap member 11 to effect the desired deflection or prestressing of the crown portion 15 of the cap member 11 as illustrated in the figures of the drawings now to be described.

FIGURES 1 to 5Seating arrangement One preferred arrangement of controlled contacting seating surfaces is illustrated in FIGURES 1 to 5 of the drawings in which both the inner wall of the crown and the main body are provided with coacting or mating seating surfaces in addition to the surfaces between the end 19 of the skirt and the shoulder 12.

Thus, main body 10 is provided at the end in assembled position adjacent the cap with a first annular seating surface 26 about the bore 22 in the main body and spaced a short radial distance outwardly thereof a groove 27 is formed in the end of the main body for mounting a spacing element 28 which forms a second annular seating surface 29 on the face thereof adjacent the inner wall of the crown in assembled position.

Similarly, the cap member 11 is formed or machined to provide coacting or mating seating members thereon as indicated by the first annular seating member 30 about the stud or connecting member 20 and spaced a radial distance outwardly thereof corresponding to the radial distance of the second annular seating surface 29 there is provided a second annular seating member 31.

The second annular seating member 31 has the free end remote from the end connected to the inner wall of the crown formed at an angle or biased with respect to the central or longitudinal axis of the main body 10 so that the radially outer edge projects an axial distance greater than the radial inner edge thereof. Further, the second annular seating member 31 extends axially a greater predetermined distance than the first annular seating member 30 to establish the clearances required for prestressing the crown 15.

The effect of this dimensional relationship is illustrated with reference to FIGURES 3 to 5 of the drawings.

Thus, FIGURE 3 shows the initial assembly position of the cap 11 on the main body 10 wherein the end 19 of the skirt 16 is in engagement with the shoulder 12 formed on the main body 10. In this position a first clearance occurs between the free end of the second annular seating member 31 and the second annular seating surface 29 and a second and greater clearance is provided between the first annular seating member 30 and the first annular seating surface 26 on the main body 10.

When nut 25 is tightened onto the threaded portion 21 of the stud or connecting member 20, the crown 15 being relatively thin will deflect to permit the outer edge of the second annular seating member 31 to come into contact with the second annular seating surface 29 formed on the spacer member 28 as is shown in FIGURE 4 of the drawings.

Further tightening of the nut 25 will cause the crown 15 to deflect still further until the inner edge of the second annular seating member 31 is in firm contact with the second annular seating surface 29 and the face of the first annular seating member 30 will also be brought into I contact with the first annular seating surface 26.

Thus, FIGURES 3 to 5 show that the radial outer portion of the angled or biased face of the free end of the second annular seating member 31 contacts first and further deflection of the crown portion causes seating of this free end and the corresponding face of the first annular seating member 30 so that any forces exerted on the outer face of the crown 15 can be transmitted to the main body 10 of the piston.

In establishing this assembly, the crown will be prestressed. This desired prestressing will in operation change only within a narrow range when working gas forces are acting on the outer face of the crown 15.

Oil cooling arrangement In order to control the relative degree of expansion of the main body 10 and to reduce the thermal stresses which occur in the ferrous alloy cap, the composite piston of the present arrangement includes an oil cooling system or arrangement for bringing oil into contact with the inner face of the crown 15 on the side remote from the face of the crown in contact with the extremes in temperatures encountered from combustion gases or other high temperature fluids when the piston is in operation.

This is accomplished by a plurality of chambers and passages which are formed between the main body and the crown 11 and in the main body 10 of the piston.

Thus, first annular seating member 30 and second annular seating member 31 projecting axially of the inner wall of the crown form a first annular groove 32 between these members and a second annular groove 33 radially outward of the second annular member 31.

The second annular groove 33 is assembled position will, with the groove 13 in the main body 11, form an outer cooling chamber 34.

Similarly, the first annular groove 32 in assembled position will form with the cap end of the main body 10 an inner cooling chamber 35 and these chambers 34 and 35 will be joined as is shown in FIGURE 1 so as to bring a suitable cooling medium such as oil into contact with the inner face of the crown of the cap 11.

Thus, the oil cooling flow system also includes passage 36 which communicates at one end with the conventional oil lubricating bearing supplied to the wrist pin (not shown). At the end remote therefrom the passage 36 communicates with the outer cooling chamber 34.

The outer cooling chamber 34 is connected through a. cross passage 37 with the inner cooling chamber 35 which communicates in turn by passage 38 with the enlarged inner bore 22 in the main body 10. Fluid from the enlarged inner bore 22 is free to pass by return passage 39 to a central chamber 40a in the main piston body 10 which is open to an oil sump or reservoir (not shown).

During operation, the flow of cooling fluid passes from passage 36 to outer cooling chamber 34 thence through passage 37 to inner cooling chamber 35. It is returned by passage 38 from the inner cooling chamber 35 to the oversized bore 22 in the main body which acts as a reservoir because the outlet of passage 38 is below the inlet or return passage 39 for returning the cooling oil to the central chamber 40a and the main oil sump (not shown). This is an advantage because on reciprocation the collected oil in the oversized bore 22 will be charged back into the inner cooling chamber 35 at top dead center which condition aids cooling of the crown 15 of the cap member at the time when the maximum heat of combustion is being transmitted to the crown.

In the present construction, it will be noted that the outer cooling chamber 34 is disposed as a shield over that portion of the skirt which contains the ring grooves 17. This serves to prevent excess heating of the ring groove of the skirt when the piston is in operation.

Hydraulic installation and removal arrangement In order to facilitate assembly and removal of the cap 11 from the main body 10 a suitable hydraulic pressure source is desirable.

Thus, referring to FIGURES 1 and 2 of the drawings a pair of spaced grooves are provided as at 40 and 41 in the face of the axially extending surface 14 about the cap end of the main body 10. Groove 40 is connected by a transverse passage 42 and an axial passage 43 to any suitable source of hydraulic pressure (not shown). The groove 41 is connected by a return passage 44 to the central chamber 40a formed in the main body 10, all of which is clearly shown in FIGURE 1 of the drawings.

In the assembly procedure, as shown in FIGURES 3 to 5 of the drawings above described, the initial position of the cap member 11 is shown in FIGURE 3. The cap will be forced onto and off the main body 10 by pressure from a suitable hydraulic source passed through the passages 43 and 42 to the groove 40 on the axially extending surface 14. This pressure is required because of the interference fit between the inner annulus 18 of the skirt portion 16 and the tapered surface of the axially extending surface 14 about the cap end of the main body 10.

The hydraulic pressure acts to expand the skirt portion 16 radially to facilitate and ease the positioning of the skirt portion into assembled position. In assembly, hydraulic pressure will be continued until the end 19 of the skirt portion 16 is tightly seated against the shoulder 12 on the main body 10 and the same will be done on disassembly until the cap member is unseated from its assembled position.

The cap member, when assembled in position, will be as illustrated in FIGURE 3 of the drawings and the spacer 23, the resilient elements or washers 24 and the nut member 25 can now be placed on the stud or connecting member 20 as shown in FIGURE 1 of the drawings.

As has been above described, when the skirt is so seated and the nut member 25 tightened, the controlled contacting seating surfaces will, by reason of the predetermined dimensions and clearances between the seating surfaces 26 and 29 on the main body 10 and seating members 30 and 31 on the cap member 11, permit the predetermined stresses or the prestressing of the crown desired for producing the advantageous results of the present invention.

Alternate constructions may be provided to produce the predetermined clearances between the main body 10 and the cap 11.

FIGURE 6seating arrangement In FIGURE 6 the cap end of the main body 10a has both the seating surface 26a and 29a on the same horizontal plane and the clearance is obtained by increasing the axial extension of the second annular seating member 31a with respect to the contacting face of the first annular seating member 30a on the cap member 11a.

The construction and operation is otherwise similar and assembly and prestressing of the crown is accomplished in the same manner as that abovedescribed for FIG- URES 1-5 of the drawings.

FIGURE 7Seating arrangement In FIGURE 7 the first and second annular seating members 30b and 31b on the inner wall of the crown have their respective seating faces disposed in the same horizontal plane while the seating surface 26b is made lower than the seating surface 29b to provide the desired clearance for the predetermined deflection or prestressing of the crown portion of the cap 11b.

The construction and assembly is otherwise similar in all respects to the form of the invention shown in FIG- URES 1 to 5 of the drawings.

FIGURE 8-Seating arrangement In FIGURE 8 the first annular seating member 30c on the cap member 11c is in the same horizontal plane as the second seating surface 290 on main body 100. The necessary clearances are provided by spacing the first annular seating surface 260 further from the surface contacting end of the first annular seating member 300 on the cap member than the second annular seating surface 290 is spaced from the second annular seating member 310.

The construction and assembly here is otherwise similar to that shown in FIGURES 1 to 5 of the drawings.

FIGURE 9Seating arrangement In FIGURE 9 the first annular seating member 30d and the second annular seating member 31d on the cap member 11d are on different horizontal planes and the clearances are provided by making the first annular seating surface 26d lower than the second annular seating surface 29d on the main body 10.

This construction, as in the case of the seating arrangement of FIGURES 6, 7 and 8, is otherwise identical to that of the form of the invention described for FIGURES 1 to 5 of the drawings.

Thus, the above disclosure has described a composite piston wherein the cap member which is made of a ferrous alloy and has a comparatively low coefiicient of the expansion is exposed to direct contact with combustion gases or extremes of heat while the aluminum alloy main body of the piston with its high coefficient of expansion is only exposed to heat conducted primarily through the controlled contacting seating surfaces.

This construction aids the bolting forces and the circumferential interference fit under all operating conditions because the low expansion ferrous alloy of the cap is operating at a higher temperature than the high expansion aluminum alloy of the main body.

The prestressing of the crown will act to relieve thermal stresses in the cap at an angle of the crown and skirt due to flexing or temperature generated dimensional changes of the crown and the forces acting thereon. These forces will be transmitted through the annular faying surfaces thus enabling the lateral component of these forces to be taken by the skirt of the composite piston with a minimum of distortion thereof.

Further, the integral nature of the crown provides a seal against dangerous combustion or other high temperature gases and reduces transmission to the skirt portion of the cap of stresses dueto bending or dimensional changes in the cap during operation.

What is claimed is:

1. A piston for an internal combustion engine comprising:

a light weight main body having a reduced portion at one end forming a shoulder and a central aperture in said main body;

a cap having a crown portion and a skirt portion about said crown portion;

a stud in said cap having one end threaded and disposed to extend into said central aperture of the main body in assembled position;

said skirt portion of the cap adapted to be seated on the shoulder of said main body; and said main body and said crown portion each having spaced seating means formed thereon; said spaced seating means disposed opposite each other in assembled position and having a predetermined clearance therebetween; and nut means to engage the threaded end of said stud to force said seating means into engagement for prestressing the crown during assembly of said cap to said main body. 2. A piston, according to claim 1, in which one of the seating means is disposed adjacent the central stud and another seating means is disposed radially outward therefrom.

3. A piston, according to claim 2, in which the seating means adjacent the central stud has a larger predetermined clearance than the other seating means.

4. A piston, according to claim 3, in which the radially outer seating means includes a tapered surface.

5. A piston, according to claim 1, in which the reduced portion of the main body and the inside of the skirt portion are tapered.

6. A piston, according to claim 5, in which the dimension of the reduced portion of the piston body is larger than the inside of the skirt portion to provide an interference fit therebetween.

7. A piston, according to claim 1, in which the crown is recessed adjacent the seating means to provide oil cooling chambers therein.

8. A piston for an internal combustion engine comprising:

a light weight main body having a reduced portion, a

seating shoulder, a plurality of upwardly facing seating surfaces, and a central aperture;

a cap comprising a crown portion and a skirt portion having a plurality of ring grooves;

the end of said skirt portion seated on said main body shoulder;

said crown portion being recessed on its inside surface to form a plurality of seating bosses;

said bosses being initially spaced from said upwardly facing seating surfaces by predetermined clearances;

a stud integral with said crown portion and extending downwardly through said central aperture;

and screw means associated with the stud to secure the cap to the body;

the clearances between the body seating surfaces and cap seating bosses being such that the crown must deflect by the action of the screw means on the central stud to permit engagement of the seating bosses on the seating surfaces thereby prestressing the cap.

9. A piston, according to claim 8, in which the recessed portions of the crown cooperate with the main body to provide oil cooling chambers for the piston.

10. A piston, according to claim 8, in which the seating boss nearer the central stud has the greatest predetermined clearance from the seating surface.

References Cited UNITED STATES PATENTS 1,747,568 2/1930 Blomgren 92220 XR 1,778,064 10/1930 Calkins 92-220 XR 2,194,097 3/1940 Reggio 922l5 2,787,505 4/1957 Laraque 92186 XR 3,385,175 5/1968 Meier 92-22O XR CARROLL B. DORITY, Primary Examiner US. Cl. X.R. 92-220 

